The invention relates to an interface device between an electrical network and electrical energy consumer systems, notably on board an aircraft, for example an aeroplane.
Current electronic systems require an interface device between an electrical network and various consumer systems which accomplish functions required of them. This interface device enables a voltage delivered by a direct current electrical network or, by extension, resulting from the rectification of an alternating voltage originating from an alternating electrical network, to the different consumer systems, but also enables them to avoid the disturbances to which the electrical network is subject. These disturbances may be network power dropouts or a power voltage below a threshold. Below this threshold the interface device no longer operates satisfactorily. In the remainder of the description the term dropout will be used, but this also encompasses a network supply voltage below the threshold.
A power reserve function, for example a capacitor, enables electrical energy to be stored, and protection to be provided against dropouts. A galvanic isolation function enables the current between two electrical circuits electrically connected to one another to be prevented from flowing.
FIG. 1 illustrates a functional diagram which places an interface device 10 between a direct current electrical network RE and a consumer system 11. At the output of the interface device 10 a modified, isolated electrical network 12, which is protected against dropouts, is obtained in this manner. The main existing solutions in terms of architecture to produce such an interface device are as follows:                use of two converter stages: the first to produce a galvanic isolation function, and the second to manage a power reserve function;        use of a converter stage allowing management of a power reserve function, and possibly a galvanic isolation function.        
In a first solution, two converter stages are used to obtain a regulated output voltage and a power reserve. An existing topology is illustrated in FIG. 2. This FIG. 2 shows several DC-DC output converters C1 to CN, for example of the “Buck” type. In the remainder of the description the term “several” means at least two. A converter of the “Buck” type, also called a serial voltage chopper, is a switched mode power supply which converts a direct current voltage into another direct voltage of lower value. As a variant, these output converters C1 to CN could be “Boost” type converters. A converter of the “Boost” type, also called a parallel chopper, is a switched mode power supply which converts a direct current voltage into another direct voltage of higher value.
Each output converter C1 to CN has two inputs; these two inputs are intended to be connected to an electrical network RE; for one of them the connection is made through a first switch 20. A capacitor Ctampon [“Cbuffer”] is connected between the two inputs of the output converters C1 to CN. These converters C1 to CN deliver regulated output voltages Vout1 to VoutN.
There is also a “Boost” type input converter 21 having two inputs connected to the electrical network RE and an output connected to an input of each of the output converters C1 to CN through a second switch 22, wherein this output is also connected to a terminal of a power reserve Cres, the other terminal of which is connected to a ground. The input converter 21 enables the power reserve Cres to be charged to a voltage higher than that delivered by the electrical network RE. The voltage delivered by the electrical network RE is called Vin.
The output converters C1 to CN enable galvanic isolation between the electrical network RE and the output voltages Vout1 to VoutN to be accomplished. They must adapt to the variations of voltage Vin of the electrical network RE, and to those of voltage Vres at the terminals of the power reserve Cres. To choose the power source of the output converters C1 to CN which accomplish the galvanic isolation it is necessary to put first and second switches 20 and 22 in place.
The first switch 20 enables the output converters C1 to CN to be disconnected from the electrical network RE, and second switch 22 enables the power reserve Cres to be connected at the input of the output converters C1 to CN. These switches 20 and 21 work in opposition. When the first switch 20 is closed, the output converters C1 to CN are powered directly by the electrical network RE. When the second switch 22 is closed, the output converters C1 to CN are powered by the electrical energy previously stored in the power reserve Cres.
The purpose of the capacitor Ctampon is to ensure that a voltage exists at the input of the output converters C1 to CN during transition phases. It is the case, indeed, that the switches 20 and 22 cannot be controlled in a strictly synchronous manner. These two switches 20, 22 therefore remain open at the same time, approximately 1 μs. Capacitor Ctampon, the value of which is much lower than that of the power reserve Cres, enables the output converters C1 to CN to be powered for several milliseconds.
This first solution has the following advantages:                It is simple, and includes two separate converter stages.        It enables a useful compromise to be found between the voltage at the terminals of the power reserve Cres and the volume it occupies.        The establishment time of output voltage Vout1 to VoutN of the output converters C1 to CN does not depend on the charge of the power reserve Cres.        The input converter 21 is dimensioned to provide only the power required to charge the power reserve Cres.        
Conversely, this first solution has the following disadvantages:                It is bulky. It comprises, indeed, n+1 converters.        It is impossible to control the current draw at start-up due to the structure of the input converter 21.        The input voltage of the output converters C1 to CN, which accomplish the galvanic isolation, may be greater than the variation of the input voltage Vin of the electrical network RE.        The losses during the switching of switch 22 are substantial; they are proportional to the capacity of capacitor Ctampon and switch 22 is subject to substantial stress during these phases.        
In a second solution, a converter is used to obtain a regulated voltage. A widely used topology is illustrated in FIG. 3. In this figure an input converter of the “forward” or “flyback” type 30 has two inputs connected to the electrical network RE and two outputs connected at the input of each of the output converters C1 to CN. The “forward” type converter is also known by the name “convertisseur direct” [direct converter] in French. The “flyback” type converter is also known by the name “convertisseur a accumulation” [accumulation converter] in French.
The output converters C1 to CN are of the same nature as in the previous example. The power reserve Cres is connected between the two outputs of the input converter 30. The input converter 30 enables the voltages at the terminals of the power reserve Cres to be regulated, and may possibly accomplish the galvanic isolation. The power reserve Cres is placed at the output of this input converter 30, requiring a substantial capacitive volume, such that a minimum voltage Vres is guaranteed, at the terminals of the power reserve Cres, during a dropout. During a dropout phase in electrical network RE, the input converter 30 is no longer functional. The output power is supplied by the power reserve Cres, which is discharging. A bypass filtering capacitor Cin is connected to the terminals of the inputs of the input converter 30.
This second solution has the following advantages:                It is simple. Indeed, it comprises a single input converter 30 having an operating range over the input voltage equal to the dynamic range of the electrical network.        
Conversely, this second solution has the following disadvantages:                The start-up time is greater than in the first solution, since the power reserve Cres must be charged for the interface to be functional.        The input converter 30 must be dimensioned to guarantee the output power, but also charging of the power reserve Cres over the allowed time.        In a steady state all the power supplied to the energy consumer systems cause losses in all converters 30 and C1 to CN.        
In conclusion, there is the same number of converters in both solutions; in the first solution the input converter 21 does not provide galvanic isolation, and in the second solution input the converter 30 can provide galvanic isolation.